iTunes 12 won't synch all my photos from Photos on my mac

I don't use iCloud for photos, I load them into my Mac's photos app and then synch them to my iPad 2 via iTunes.

This has worked for years, until iTunes 12, when it only synchs around 80% of the photos.

I tried unchecking sync photos, and the first time iTunes removed them from the iPad ok. When I added them again, it still only synch'd 80%.

I tried again and this time iTunes didn't remove the photos from the iPad at all.

So I did a hard reset on the iPad and restored from backup. Great - photos were removed from the iPad.

But when I added photos to synch, only 80% were transferred.

Before I hard reset and rebuild from scratch, does anyone know why this is happening and anything else I could try?

I'm sure Apple want me buy a new iPad!